Generally, an igniter is used to start an exothermic reaction, such as combustion, deflagration, or detonation. For example, an igniter is widely used to start inflating an air bag of an automotive or to start firing industrial explosives.
The igniter includes a bridge part that generates heat by being energized, an ignition compound ignited by this heat generation, and electrode pins used to energize the bridge part. To ignite the ignition compound, a conventional igniter has used a bridge wire as the bridge part. The bridge wire is a thin wire that has electric resistance and that is disposed between two contact points. The ignition compound surrounds the bridge wire, and is ignited by ohmic heating when the bridge wire is supplied with an electric current.
The conventional igniter provided with the bridge wire uses a nichrome wire as the bridge wire. If the wire diameter of the bridge wire is extremely small, this bridge wire cannot be provided in the igniter. If the wire diameter of the bridge wire is large enough to be provided in the igniter, this bridge wire has a great thermal capacity, and hence time from the bridge wire is energized till the bridge wire reaches an ignition temperature will become long. Therefore, for example, a high-speed responsiveness required for an automotive side inflator is not satisfied.
The term “semiconductor bridge” is a general term for bridges produced by semiconductor technology, such as evaporation. The structure of the semiconductor bridge is made up of two electrode pads each of which serves as an electric contact point, two electrode parts disposed under the electrode pads, and a bridge part through which the two electrode parts are connected together, which is ignited by being energized, and which is thinner than the electrode parts. The semiconductor bridge used in the igniter is a thinner film bridge whose thickness is about several microns than the bridge wire, and hence can make the thermal capacity small, and can give a high-speed responsiveness. The bridge wire allows an ignition compound to be ignited in about 800 to 1000 microseconds, whereas the semiconductor bridge allows an ignition compound to be ignited in about 100 to 200 microseconds in most cases. Therefore, the semiconductor bridge enables high-speed ignition.
An example of such a semiconductor bridge is disclosed by Patent Document 1. The semiconductor bridge disclosed by this document has a heat insulating layer disposed on the whole surface of a base. An electrically-conductive ignition bridge layer that has undergone patterning is disposed on the heat insulating layer, and can be ignited by less energy. In the ignition bridge layer, hydrogenated hafnium or hydrogenated titanium is used as an essential ingredient.
Patent Document 1: Japanese Translation of International Application (Kohyo) No. 2001-505646